Diesel fuel



Patented Feb. 4, 1941 2,230,817 nmsm. FUEL Bernard H Shoemaker, Hammond, Ind., assignor to Standard Oil Company, Chicago, III-, a cor- Duration of Indiana No Drawing? Application December 21, 1936, Serial No. 116,995. Renewed December 7, 1939 9 Claims. (01. 44-9) This invention relates to improvements in fuels, in particular, to improvements in Diesel engine fuels.

The process of combustion which occurs in the Diesel engine is very complex and is more com plicated than that in gasoline internal combustion engines because the liquid fuel is injected directly into the cylinder. On injection the oxidation of the fuel first takes place very slowly 'but because of its exothermic nature, the reaction accelerates and soon reaches a point when the rate of heat generation by oxidation is greater than the heat dissipation, and a flame is established. The interval between the time the fuel is injected into the cylinder and the time the fuel becomes ignited is the so-called delayed period or ignition lag. Better engine performance is obtained when the delayed period or ignition lag is of short duration. Following the ignition lag or delayed period there is a period of ignition accompanied by a period of very rapid pressure rise. At the end of this second stage the temperature and pressure within the cylinder is so high that any fuel remaining to be injected 25 during this period burns as it enters the cylinder.

In all cases the aim is to keep the delayed period as short as possible for the sake of smooth running or to keep the roughness of running or Diesel knock at a minimum. This requires a 30, Diesel fuel of good ignition characteristics.

It is an object of this invention to provide an improved Diesel engine fuel.

It is another object of this invention to provide a Diesel engine. fuel having improved ignition properties.

It is a further object of this invention to provide a method of obtaining an improved Diesel engine fuel having improved ignition characteristics.

Other objects and advantages of this invention will become apparent from the following description thereof.

As hereinbefore stated the process of combustion in a Diesel engine may be divided into three 45 distinct stages: (a) the delay period, (b) a period of rapid combustion, and (c) a period in which the rate of combustion may be controlled by the fuel pump and nozzle. The smoothness of running or knocking obtained in any fuel being so determined by the extent of the delay which it gives in the first stage and consequently a maximum pressure which it develops in the second stage is therefore dependent upon the ignition properties of the fuel.

I have discovered that the ignition characteristics of Diesel fuels, particularly hydrocarbon distillate fuel oils adapted for Diesel type engines, may be improved and correspondingly the cetene number of Diesel fuels increased when 0.01 to 1.0% of a mercaptan is added to the oil before 5 the same is treated with sodium plumbite solution and sulfur (doctor solution). Suflicient sodium plumbite and sulfur, the amount of sulfur being about to 350% in excess of the theoretical amount required, should be used to decom- 1 pose all of the mercaptan. The mercaptans used may be either aliphatic, aromatic or aralkyl mercaptans, such as ethyl mercaptan, tertiary butyl mercaptan, isobutyl mercaptan, secondary amyl mercaptan, tertiary amyl mercaptan, benzyl mercaptan, phenyl mercaptan, etc.

My invention may be illustrated by the following specific example: A liter of a hydrocarbon distillate fuel having a boiling range between 400 and 750 F. to which has been added about 4.13 grams of tertiary butyl mercaptan was treated with sodium plumbite solution and sulfur using a total of about 2.25 grams of sulfur. The amount of mercaptan used was equivalent to about 0.5% by volume of the hydrocarbon distillate and the sulfur used was equivalent to about 300% of the theoretical requirement. When. the reaction was completed the spent sodium plumbite solution was settled out and the oil layer washed several times with water. 30

The ignition properties or the knocking properties of Diesel fuels may be determined by comparing the knock induced by the fuel in question with a standard fuel. The recognized standard fuel is a blend of cetene or cetane and alpha methyl naphthalene. Cetene or cetane used as 8. Diesel fuel have excellent ignition properties and therefore produces little or no knock, whereas alpha methyl naphthalene is a knock inducer. The fuels are compared by blending cetene or cetane and alpha methyl naphthalene until a knock corresponding to the knock in the reference fuel is obtained. A Diesel fuel of good ignition properties is therefore comparable to a blend containing a large percent of cetene or cetane. The fuels are rated in terms of cetene numbers or cetane numbers which are equal to the percent by volume of cetene or cetane in the mixture of cetene or cetane and alpha methyl naphthalene which is equivalent in Diesel knock rating of the fuel under test. It follows, therefore, that a Diesel fuel having a high cetene number or cetane number has good ignition characteristics and is therefore a desirable Diesel fuel.

A sample of a hydrocarbon distillate fueloil Treated without mercaptan Treated 1 with mercaptan Improvement Fuel

Cetane number Oetene number,

From the above results it is seen that a substantial increase in both cetane and cetene numbers is obtained when the Diesel fuel is treated with doctor solution in the presence of a mercaptan.

Diesel fuels treated in the manner herein described may be used as such or the treated Diesel fuel may be blended with an untreated stock to improve the ignition characteristics of the lat ter. The proportions in which the Diesel fuels are blended depends upon the relative ignition characteristics of the treated and untreated stocks and the desired cetene number.

.While I prefer to use 0.01% to 1.0% of the mercaptan in my process, more than 1% of the mercaptan may be used without departing from the spirit and scope of my invention. The addition of more than my preferred quantity of mercaptan, however, causes sweetening difliculties and is therefore undesirable.

While I have described my invention in terms of a preferred embodiment thereof, the same is not to be taken as a limitation of the scope thereof but fllustrative thereof, except as defined in the appended claims which should be given the broadest interpretation permitted by the prior art.

I claim:

1. The method of improving the ignition characteristics of 9. Diesel fuel comprising treating a Diesel fuel distillate with a mixture of sodium plumbite solution and sulfur in the presence of added mercaptan, said sulfur being used in quantities ranging from about 50% to about 350% in excess of the theoretical amount required to sweeten said distillate.

, 2. The method of improving the ignition characteristics of a petroleum Diesel fuel oil, comprising treating a fuel oil distillate with amixture of sodium plumbite solution and s'ulfur in the presence of an added alkyl mercaptan; said sulfur being used in quantities ranging from about 50% to about 350% in excess of the theoretical amount required to sweeten said distillate.

3. The method of improving the ignition characteristics of a petroleum distillate fuel oil adapted for the operation of Diesel type engines comprising treating said distillate with a mixture of sodium plumbite solution and sulfur in the presence of added tertiary butyl mercaptan,

the amount of sulfur required to sweeten the mixture being about 300% of the theoretical amount of sulfur required to decompose-all ofthe mercaptans to disulfides.

4. A method of improving the ignition characteristics of petroleum Diesel fuels comprising adding a mercaptan to a petroleum oil fraction boiling above the gasoline range and subsequently treating the mixture of oil and mercaptan with a mixture of sodium plumbite solution and sulfur, the amount of sulfur used in said mixture being about 50% to about 350% more than the theoretical amount required to decompose all of the mercaptans present to disulfides.

5. The method of improving the ignition characteristics of a petroleum fuel oil distillate adapted for the operation of Diesel type engines comprising adding tertiary butyl mercaptan to said distillate and subsequently treating the mixture of fuel oil and tertiary mercaptan with a mixture of sodium plumbite solution and from 50% to 350% more sulfur than the theoretical amount required to sweeten said distillate.

6. The method of improving the ignition characteristics of a hydrocarbon distillate fuel oil adapted for the operation of Diesel type engines comprising adding tertiary butyl mercaptan to said distillate and subsequently treating the mixa ture of oil and tertiary mercaptan with a mixture of sodium plumbite solution and about 300% more sulfur than the theoretical amount required to sweeten said distillate, separating the spent sodium plumbite solution from the treated oil and washing said treated oil with water.

7. The method of improving the ignition characteristics of hydrocarbon distillate fuel oils adapted for use in. Diesel engines which comprises adding 0;01% to 1.0% of a mercaptan to said distillate and subsequently treating said mixture with a mixture of sodium plumbite and sulfur, said sulfur being used in quantities of 50% to 350% in excess of the theoretical amount required to decompose all of the mercaptan.

8. The method of improving the ignition characteristics of hydrocarbon distillate fuel oils having a boiling range of between 400 and 750 F.

adapted for the operation of direct injection in internal combustion engines which comprises adding 0.5% by volume of tertiary butyl mercaptan to said distillate fuel oil, treating said mixture with sodium plumbite solution containing about 300% of the theoretical amount of sulfur required to decompose all of the mercaptan, separating the spent sodium plumbite solution from the treated oil and subsequently washing said treated fuel with water.

9. A Diesel fuel obtained by treating a petroleum distillate fuel oil having'a boiling range of between 400 and 750 F. with a mixture of sodium plumbite and sulfur in the presence of added mercaptan. the amount of sulfur used being from about 50% to about 350% in excess of the theoretical amount required to sweeten said distillate.

BERNARD H. SHOEMAKER. 

